Obtaining accurate three-dimensional (3D) images of a target using a two-dimensional (2D) video camera subsystem integrated with a three-dimensional lidar (laser radar) subsystem is difficult unless the two subsystems are calibrated with one another. Calibration may refer to the registration of the two subsystems with one another such that measurements of points on a surface of the lidar subsystem are related to the 3D accurate coordinates of a target, which in turn are accurately mapped to the same points as measured by the video subsystem (or substantially so within the measurement tolerances, etc., of each subsystem). In other words, accurate three-dimensional images require correspondence between measurements of the 3D coordinates obtained from the lidar subsystem with the respective pixel positions in the 2D video image.
Factory calibration of the subsystems may be useful in obtaining an initial registration between the lidar subsystem and the video subsystem. However, because both the lidar subsystem and the video subsystem employ various mechanical components, the calibration may change as a result of various relative mechanical changes occurring within the lidar subsystem as well as between the lidar subsystem and the video subsystems, including, but not limited to mishandling, temperature fluctuations, mechanical strains, and other mechanical effects as would be appreciated. In particular, various moving mechanical parts included in or associated with the lidar subsystem (e.g., scanning mirrors and their alignment to one another and also to the laser beams) are susceptible to such changes.
What is needed is an improved system and method for calibrating the video and lidar subsystems of a three-dimensional measurement system.